May be a dumb question - Poe Injectors

[eggzlot]

I am trying to test something with cameras on another network - long story.  Usually they are plugged into a Cisco PoE and they work.  I am looking at Lilin 7722  and a Lilin 6022 - older models installed in late 2013.  I forget if they are models with E or X at the end but older 2MB/1080p type cameras.  

If I need to use a PoE injector now for them can I fry them by using too big of a PoE injector or they only take in as much power as they need?  I do not want to fry the cameras.  Is it just an under powered PoE injector wont power the device but an over powered PoE injector wont fry the device?  Or can an over powered Poe injector fry the device?

Stupid question but not looking to fry my camera, cause an electrical fire, break my switch, etc.

Thanks!